Zack was aboard Oceanic Flight 815 traveling to Los Angeles, CA to see his mother, and was traveling with his sister Emma. After the tail-section crashed into the water he was pulled out by Mr. Eko, and alerted him to his sister’s body which was floating in the water. Zack apparently has a close bond with Emma, because he immedantly screams for her after the crash and quickly points to her body in the water. Libby and Cindy would often watch over the two when danger would strike. Zack lived with the tail-section's survivors until Day 12 when he was abducted by The Others. His name and description was on a list of other survivors found in the pocket of the woman Ana-Lucia killed defending herself. (The Other 48 Days)

During their time with the Others, Emma and Zack spent time with Juliet. During a conversation with Ben, Juliet revealed that the two had been asking about their mother, to which Ben replied that they would stop in time. Ben also revealed that Zack and Emma were on the "list". (The Other Woman)

Zack later showed up with his sister Emma, as well as Cindy and the rest of the captured Tail Section survivors outside of Jack's cage. When Jack suddenly became enraged and demanded that they leave. Zack proceeded with the rest of her group away from the cages, and was seen with the same teddy bear he had with him on the day of the crash. (Stranger in a Strange Land)

Zack, Emma and Cindy later setup camp with the rest of the Others, and retreated back across the island the morning after Locke was unable to murder his father. (The Brig)